Kim Jung-ju, founder of South Korea’s biggest game maker Nexon, passed away on Monday. He was 54.

Nexon’s holding company NXC said Tuesday evening that Kim died in Hawaii, US, on Feb. 28. He had been undergoing treatments for depression and it appeared that the symptoms had become worse as of late, it said. The cause of death was not given.

Nexon CEO Owen Mahoney paid condolences to Kim.

“It is difficult to express the tragedy of losing our friend and mentor Jay Kim, a man who had an immeasurably positive impact on the world,” said Mahoney, using Kim’s English name. “As a founder and visionary leader, Jay encouraged those around him to ignore the skeptics and trust their creative instincts. He will be deeply missed by his Nexon family and many friends.”

Kim founded Nexon in 1994, and launched the world’s first multiplayer online role-playing game The Kingdom of the Winds. The company later showcased popular hit titles such as MapleStory, KartRider, Mabinogi and Dungeon & Fighter.

The game developer went public on the Tokyo Stock Exchange in 2011. Following the listing, Nexon became the first Korean gaming company to surpass 1 trillion won ($830 million) in annual sales the year it went public. Nexon currently offers more than 45 games in 190 countries.